Currently, the majority of vegetable oil production (estimated at 87 million metric tons with approximate market value of 40 billion U.S. dollars) goes into human consumption, with as much as 25% of human caloric intake in developed countries being derived from plant fatty acids. In addition to their importance in human nutrition, plant fatty acids are also major ingredients of nonfood products such as soaps, detergents, lubricants, biofuels, cosmetics, and paints. With the accelerating costs of petroleum, vegetable oils provide an increasingly cost-effective alternate source for raw materials.
Selecting plants for increased (and decreased) oil production by classical genetic selection methods has been ongoing for at least a century. Indeed, the complexity in determining trait-genotype associations for the seemingly simple trait of oil production has been demonstrated. For example, Laurie et al. (2004) “The Genetic Architecture of Response to Long-Term Artificial Selection for Oil Concentration in the Maize Kernel” Genetics 168:2141-2155 describe an association study that involved selection of the maize kernel for the simple phenotype of altered oil concentration, over a period of more than a century (one of the longest running selection experiments in biology). The association study detected about 50 “quantitative trait loci” (QTL) that contributed to changes in oil concentration over the 100+ year period, together accounting for only about 50% of the observed variance (suggesting that even more than the 50 identified QTL influence the oil concentration phenotype). The individual QTL effect estimates for the identified QTL were small and largely additive. In the oil phenotype experiment described by Laurie et al., the populations changed from a 4.7% oil content at the beginning of the experiment to a 19.3% oil content at the end, among the lines selected for high oil content, and a 1.1% oil content in the lines selected for low oil content.
The biochemical study of de novo fatty acid biosynthesis in plants is, thus, fundamentally important and practically essential for the metabolic engineering of fatty acid biosynthesis in agronomically important crops (see also, Thelen and Ohlrogge (2002) “Metabolic engineering of fatty acid biosynthesis in Plants,” Metabolic Engineering 4: 12-21; Scowl et al. (1999) “Genetic engineering of plant lipids,” Annu. Rev. Nutr. 19: 197-216). In plants, the majority of fatty acids are biosynthesized in the plastid. Over the last two decades nearly all aspects of fatty acid metabolism in plants have been uncovered. However, one of the remaining questions that has thus far resisted elucidation is how free fatty acids are transferred from an inner thylakoid membrane to an outer envelope of a plastid, where they are reactivated to acyl-CoAs for utilization in cytosolic glycerolipid synthesis. Without knowledge of how this mechanism works, efforts to increase, flux through fatty acid synthesis pathways by metabolic engineering have been hampered.
The present invention overcomes these previous difficulties, by providing a new family of chalcone-isomerase like genes that encode fatty acid binding proteins that, e.g., assist in transport of fatty acids from the thylakoid membrane to the outer plastid envelope. These and other features of the invention will be apparent upon review of the following.